Etching process.



H. WI. WILLIAMSON.

ETCHING PROCESS.

APPLICATION FILED NOV. 6, I9I2.

1 9 1 8,876 Patented June 27, 1916.

2 SHEETS-SHEET I.

H. M. WILLIAMSON.

ETCHING PROCESS.

APPLICATION FILED NOV. 6' 1912.

1,1 8,870. Patented June 27, 1916.

2 sHEETS-SHEET 2.

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HARRY M. WILLIAMSON, OF DENVER, COLORADO, ASSIGNOR TO B. E. WILLIAMSON, OF

DENVER, COLORADO.

ETCHING PROCESS.

To all whom it may concern:

Be it known that I, HARRY M. WILLIAM- SON, a citizen of the United States, residing at Denver, in the county of Denver and State of Colorado, have invented certain new and useful Improvements in Etching Processes, of which the following is a specification.

This invention relates to a process for etching metal printing plates and it has for its object the provision of a simple method of etching cpppenand other metallic plates, which in quickness of action, far exceeds the old methods of etching by means of a rocking tray or a hand brush, wh1ch produces a printing surface at once sharp, deep and even and which protects the workmen from the harmful effects of the noxious and dangerous acid fumes.

Of the methods of etching printing plates at present most commonly used, those of etching by means of a rocking tray and of brushing the printing surface of a submerged plate, are slow and uncertain in their action and that of subjecting the etching surface of a plate to the influence of an aerated acid spray is objectionable in that 1t requires the employment of an expensive, complicated and easily deranged apparatus and in that the surface of the plate is continuously subjected to the corrosive action of the acid.

Practical demonstrations have proven that to obtain the most speedy and satisfactory results in a process of etching printing plates, it is essential that the etched metal scum which constantly forms upon the etching surface be speedily removed to keep the work clean and remove every obstruction to the proper action of the acid and that the oxygen necessary in the etching process is brought in direct contact with the surface of the plate. Both these requirements are effectively attained in the practice of my process which, briefly, consists in brushing the etching surface of a submerged plate with an air blast'which being made to move back and forth across said surface removes the scum formed thereon, and by temporary displacement of the acid brings at the same time fresh oxygen in direct contact w1th the same. The brushing action of the moving blast of air, entirely removes from the surface of the plate all scum, impurities Serial No. 729,749.

and coatings such as the metallic lead coatmg formed on zinc plates, without any poss1ble lIl]1lIy to the resist or coating which protects the image on the plate. The forcible introduction of oxygen into the solution in close proximity to the etching surface of the plate, or at the very point at which in etching copper plates, ferrous chlorid is beng formed, keeps the solution oxidized to its hlghest point, and inco'nsequence maintalns the same constantly at its maximum activity with the result that the etching act1on of' a given solution on the plate is greatly expedited. In addition; to the oxidizing and brushing actions of the blast of air, its introduction in the mannerstated, has a cooling effect on the plate by reason of the expansion at the surface of the metal of highly compressed air, and evaporation of the water of the solution at the said surface, and this cooling effect expedites the etching process as it permits of the plate being subjected to a more vigorous and rapid action of the acid without injury to the resist or coating which protects the image on the plate. In the accompanying drawings I have shown an apparatus suitable for use in the practice of my process, it being understood that the construction and arrangement of the essential elements of the same may be varied within the spirit of my invention.

In the drawings, in the various views of which like parts are similarly designated, Figure 1 represents a plan view of the apparatus, Fig. 2, a section taken along the line 22, Fig. 1, Fig. 3, a transverse section along the line 33, Fig. 1, Fig. 4, a fragmentary section similar to Fig. 2, showing a modified form of the traveling carriage comprised in the construction, and Fig. 5, a fragmentary, sectional view of a printing plate, the acid in which it is submerged, and an air blast, all drawn to an exaggerated scale.

Referring more specifically to the drawings, the numeral 2 designates a shallow tray which is composed of or lined with a non-corrosive substance to withstand the action of the acid. A rectangular frame 3 which is adapted to support a printing plate 4: in spaced relation to the bottom surface of the tray is suspended from the upper edge of the same by means of a second frame operativel 5 with which it is rigidly connected. Secured upon standards 6 which are erected upon the upper frame 5, are two pairs of rails 7 between which a wheeled carrier 8 has a reciprocating movement; a flaring nozzle 9 is secured in a substantially upright position in connection with a flexible conduit 10 and it has in its lower end an outlet slot which extends transversely to the direction of its movement for the ejection of a blast of air onto the etching face of the plate.

A pair of cams 12 disposed adjacent the outer end surfaces of the tray are eccentricall mounted upon a shaft 13 which exten s through alined openings in the ends of the tray and the nozzle 9 and which at one of its extremities is provided with a handle 14. Ledges 15 on the frame 5 are disposed to be engaged by the peripheral surfaces of the cams 12 when the shaft 13 is rotated by means of the handle 14, the object of this feature of the invention being to raise the plate 4 together with the nozzle 9 above the surface of the acid contained in the tray when it is desired to interrupt the etching process. A crank shaft 16 mounted in suitable bearings 17 in proximity to the tray, carries a crank wheel 18 whose wrist is formed u on a block 19 which being slidably mounte in a radial, dovetailed guide-way 20 on the wheel, may by means of an endless screw 21, be adjusted to any desired distance from the center of the same, to vary the movement of the carriage in accordance with the width of the printing plate disposed in the tray. The shaft 16 is provided with a pulley 22 which through the medium of a belt 23, receives its rotary movement from a conveniently located driving element, and a pitman 24 connects the wrist of the crank wheel wit the carriage 8.

To rotect the operator against the harm ful effects of the acid fumes, I preferably inclose the apparatus in a casing 25 which by means of a chimney 26, connects with the atmosphere outside the room in which the etching process is carried on and this casing may be rovided with one or more windows 27 or, if so desired, with a glass top to enable the workman to observe the effects of the etching process on the surface of the plate. Located below the tray are a plurality of acid tanks 28 which are provided with fluid-lifting devices by which their contents may be transferred to the tray and which are separately connected with an out let opening at the lowest point of the sloping bottom of the latter by means of valvecontrolled conduits 29.

The lifting devices above 'referred to, each consists preferably of a pipe 30 which extends from the bottom-portlon of the re spective tank upwardly to a point above the tray and which has its upper portion bent downwardly to deliver the fluid into the same. second pipe 31 extending into the tank connects with a header 32 which by means of a branch pipe 33 is connected with a discharge conduit 34 of a compressor or reservoir of air under pressure to which the flexible tube 10 of the nozzle is likewise attached. Valves 35 are applied at different points in the various conduits to direct the flow of air to any one of the tanks 28 or to the nozzle 9, as may be desired.

In the practice of my process the metallic plate 4 is disposed upon the lower member of the support composed of the connected frames 5 and 3 below the surface of the acid contained in the tray. The nozzle 9 is placed in communication with the source of air under pressure by opening the proper valve in the conduit 34 which connects it with the rotation of the crank shaft, moved to and fro at a comparatively slow rate of speed. The air discharged through the nozzle in a transversely extending blast, temporarily displaces the acid in which the plate is submerged and engages the bared portion of the etching surface of the latter, as shown in Fig. 5, thus removing the scum formed on the said surface and at the same time, supplying the oxygen required in the etching process. The nozzle moving to and fro causes the air blast to brush the surface of the plate from one end to the other, it being understood that the acid temporarily displaced by the action of the air, is immediately replaced by the acid which follows the blast as it travels along the late.

It-is essential that the an is discharged from the nozzle so as to engage the printing plate at right angles to its etching surface as lllustrated in Fig. 5 of the drawings, whereby to prevent undercutting of the dots or ralsed portions of the printing surface and the consequent formation of weakened and undersized or ragged dots.

In etching plates of large dimensions, the process may be expedited by providing the carriage with a plurality of nozzles communicating with a common source of air supply, as is shown in F i 4, and it will be understood that while 1n the drawings, the nozzle has been shown to extend above the acid bath, it may if so desired, be immersed therein to deliver the air blast beneath its surface and that within the spirit of my in vention the nozzle may be held stationary and the plate or the bath in which it is sub merged, reciprocated, or any other suitable means may be employed to subject the surface of the plate alternately to the influence of acid and air. By turning the shaft 13 by means of the handle '14 the plate 4.- ma be lifted above the surface of the acid wit out interrupting the flow of air through the nozzle and the etching process may thus be instantly discontinued as the blast of air after the plate has emerged from the acid bath will immediately remove any fluid remaining on the surface thereof.

The tanks 28 are, in practice filled with acid solutions of different strength and by their connections with the tray, provide a convenient means for changing the acid bath in accordance with the character and requirements of the plate or plates under treatment.

Having thus described my invention what I claim and desire to secure by Letters-Patent is:

1. The process of etching printing plates consisting in moving a blast of air across the etching surface of a plate submerged in acid, while forcibly engaging the same.

2. The process of etching printing plates consisting in directing an elongate blast of air onto the etching surface of a printing plate submerged in acid, and moving said blast across said surface in a direction transverse to its longitudinal extent.

3. The process of etching printing plates consisting in directing air under pressure onto a surface of a printing plate submerged in acid, at right angles to said surface.

4. The process of etching printing plates consisting in brushing the etching surface of a printing plate submerged in acid, with a blast of air directed at right angles to said surface.

5. The process of etching printing plates consisting in forcibly engaging the etching surface of a plate submerged in acid, with a blast of air directed onto the plate at right angles to said surface.

In testimony whereof I have atfixed my signature in presence of two witnesses.

HARRY M. VILLIAMSON.

Witnesses:

CHAS. H. BROWN, F. A. Moss. 

